1. Technical Field
The present invention relates to a novel nano-composite structure, which consists of an amorphous matrix with embedded nano-crystallites. The nano-composite structure features high density, low grain boundary volume and no voids, in a bulk or film format, for a wide range of applications. Present invention is especially important in certain technology areas, such as transparent optical ceramics, transparent display, protection armor, nuclear protection, pulsed power, high voltage electronics, high energy storage system, and high power microwave systems. It also relates to processes to fabricate the said structure.
2. Technical Background
Nano-composite materials have been recognized as having tremendous potential in many technical sections owning to their unique and/or superior physical properties to those of the corresponding bulk or nanocrystalline materials. In general, pre-produced nano-crystallites are mixed into polymer or glass matrix to form the nanocomposite structure. However, there are some big technical challenges in processing of the nanocomposite structures to meet various technical requirements, e.g., a material with low defect microstructure, which is very important for many applications, such as transparent optical ceramics, protection armor, nuclear protection, high voltage applications, pulsed power, high energy storage system, high power microwave systems, power electronics, etc.
One of the biggest concerns is the level of agglomeration of the pre-made nano-crystallites, because of the extremely small particle size and hence the large surface area, the nano-crystallites tend to form agglomerates to reduce surface energy, that lead to undesired material defects and processing complications, which certainly affect the material performance. The differences in chemical, optical and/or mechanical properties between the matrix and the nano-crystallites can also produce issues in certain area of applications. For instance, a large variation in optical index between matrix and nano-crystallites lower the transparency of the nano-composite materials.
This invention solves the problems involving precipitating nano-crystallites in an amorphous matrix to form a nanocomposite structure, in which the nano-crystallites are precipitated from the matrix and are self-assembled without forming agglomerates or clear grain boundaries.
The amorphous matrix and the nano-composite structure can be formed in a bulk of thin film format, by heating of a solution mixture of metal salts or metalorganic compounds, or a mixture of non-crystalline compounds, at relatively low temperatures. The mild processing conditions are especially beneficial in terms of lowering cost or making possible of non noble electrodes in subsequential processing of electronics.
The nano-composite structure, instead of a frilly crystallized ceramic one, features low grain boundary volume and few voids. Those are very important characteristics for a wide range of applications. Grain boundaries in polycrystalline materials, structural mismatches in the interfaces, and voids due to impropriate processing are the sources for defects.
The nano-composite structure can possess superior electrical, mechanical and optical properties because of the absence of grain boundaries that could act as scattering sources and energy traps, or cause electrical breakdown. Excellent optical properties of the nano-composite thin films, including high transparency (>80% in visible range), bright upconverting luminescence, and smooth surface, have been demonstrated.